The disclosure of Japanese Patent Application No. 2002-156347 filed on May 29, 2002, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a valve opening/closing timing control apparatus and method.
2. Description of Related Art
A conventional valve opening/closing control apparatus is disclosed in Japanese Patent Laid-Open Publication No. 2000-320356. This apparatus includes a camshaft whose rotation is synchronized with opening/closing timing of an intake valve or an exhaust valve in an internal combustion engine, a relative rotation angle adjustment mechanism which transmits torque of a crankshaft in the internal combustion engine to the camshaft and which adjusts a relative rotation angle between the crankshaft and the camshaft, and a lock mechanism which utilizes hydraulic fluid, and which mechanically locks or unlocks the relative rotation angle that is adjusted by the relative rotation angle adjustment mechanism.
In the internal combustion engine in which an intake stroke, a compression stroke, an explosion stroke and an exhaust stroke are repeated, a rotational position of the crankshaft indicates timing of each stroke. Accordingly, valve opening/closing timing in each stroke can be controlled by transmitting the rotational position of the crankshaft to the camshaft. When the relative rotation angle between the crankshaft and the camshaft changes, opening/closing timing of the valve which opens or closes in synchronization with rotation of the camshaft changes. Accordingly, pressure inside a cylinder of the internal combustion engine can be changed to a desired value, and efficient driving can be performed.
In this case, the relative rotation angle is locked by the lock mechanism at the start time of the internal combustion engine. The lock mechanism in the locked state can be unlocked by hydraulic fluid.
However, sometimes at the start time of the internal combustion engine, the lock mechanism in the locked state cannot be unlocked promptly. At such times, when the rotation angle is adjusted, load is placed on the lock mechanism because it is still locked. In cases where the lock mechanism can be promptly unlocked, or in the case where the lock mechanism has been unlocked, if the relative rotation angle is not adjusted for a long time (for example, if adjustment is always delayed by a predetermined amount in order to ensure that the lock mechanism will be in the unlocked state), efficiency and operating performance of the internal combustion engine cannot be enhanced.
The invention is made in consideration of such a problem. It is one object of the invention to provide a valve opening/closing timing control apparatus and method which is capable of enhancing efficiency and operating performance of an internal combustion engine.
The valve opening/closing timing control apparatus and method according to the invention can be used with a camshaft whose rotation is synchronized with opening/closing timing of an intake valve or an exhaust valve of an internal combustion engine, a relative rotation angle adjustment mechanism which transmits torque of a crankshaft of the internal combustion engine to the camshaft and which adjusts a relative rotation angle between the crankshaft and the camshaft, and a lock mechanism which utilizes hydraulic fluid, and which selectively mechanically locks or unlocks the relative rotation angle that is adjusted by the relative rotation angle adjustment mechanism.
As an exemplary embodiment of the invention, a valve opening/closing timing control apparatus and method operates such that, when the lock mechanism is in the locked state and the internal combustion engine is started, a controller implementing the inventive method determines a duration of a time period from a start of the internal combustion engine until a start of relative rotation angle adjustment by the relative rotation angle adjustment mechanism based on an unlocking force of the hydraulic fluid which is applied to the lock mechanism. As used herein, the term xe2x80x9ccomputationxe2x80x9d includes extraction of a value using a map (using a look-up table), as well as other forms of computation, for example, in which equations are solved.
In this control apparatus and method, after the start of the internal combustion engine, when the lock mechanism is difficult to unlock, relative rotation angle adjustment is delayed so as to protect the lock mechanism. Meanwhile, when the lock mechanism can be promptly unlocked, the relative rotation angle is promptly adjusted.
Namely, when the unlocking force of the hydraulic fluid which controls the lock mechanism is small, the lock mechanism cannot be promptly unlocked. Accordingly, the lock mechanism is protected by delaying relative rotation angle adjustment (by extending the duration of the above-mentioned time period). Meanwhile, when the unlocking force of the hydraulic fluid is large, the lock mechanism can be promptly unlocked. Accordingly, relative rotation angle adjustment is promptly performed (the duration of the above-mentioned time period is shortened), and a preferable valve opening/closing timing is realized promptly. As a result, efficiency and operating performance of the internal combustion engine can be enhanced.
In the above-mentioned case, it is assumed that relative rotation angle adjustment relates to unlocking of the lock mechanism, that is, unlocking control is subject to adjustment control to a certain extent. However, even when relative rotation angle adjustment is independent of unlocking of the lock mechanism, the above-mentioned effect can be obtained. More particularly, it is possible to configure a relative rotation angle adjustment mechanism which is capable of completely unlocking the lock mechanism before relative rotation angle adjustment, that is, a relative rotation angle adjustment mechanism which is capable of controlling adjustment and unlocking independently. In this case, since it can be estimated that unlocking of the lock mechanism is incomplete when the unlocking force is small, the lock mechanism can be protected. Also, since it can be estimated that unlocking of the lock mechanism is complete when the unlocking force is large, preferable valve opening/closing timing can be promptly realized.
In this case, the unlocking force signifies a degree of promoting unlocking by the lock mechanism. The unlocking force may be either an instantaneous value or an integrated value. Also, the hydraulic fluid is oil in the case of hydraulic pressure control. However, the hydraulic fluid may be another fluid.